Is there any example or guide to start using PnP-JS-core in the forms? Sharepoint Online.
I've been looking for a while without luck!
This is the PnP Core starting point
This library makes calling REST endpoints easier,
then those technologies are your starting point.
You can find here all the documentation of Office Dev PnP: https://dev.office.com/blogs/PnP-November-2016-Release
And here you can follow interested tutorials videos: http://aka.ms/sppnp-videos